1. Field of the Invention
The present invention relates to a charged particle beam lithography apparatus and a charged particle beam lithography method and, for example, relates to a charged particle beam writing apparatus and a charged particle beam writing method for correcting dimension variations due to a proximity effect.
2. Related Art
Lithography technology in charge of development of more microscopic semiconductor devices is an extremely important process among semiconductor manufacturing processes that solely generates patterns. In recent years, with increasingly higher integration of LSI, a circuit linewidth demanded for semiconductor devices is becoming finer year after year. To form a desired circuit pattern on such semiconductor devices, a high-precision original pattern (also called a reticle or mask) is needed. Here, electron beam lithography technology has essentially an excellent resolution and is used for production of high-precision original patterns.
FIG. 7 is a conceptual diagram illustrating the operation of a variable-shaped electron beam writing apparatus. The variable-shaped electron beam (EB) writing apparatus operates as described below. First, a first aperture plate 410 has an oblong opening, for example, a rectangular opening 411 for shaping an electron beam 330 formed therein. A second aperture plate 420 has a variable-shaped opening 421 for shaping the electron beam 330 that passed through the opening 411 into a desired oblong shape shaped therein. The electron beam 330 that passed through the opening 411 after being irradiated from a charged particle source 430 is deflected by a deflector. Then, the electron beam 330 passes through a portion of the variable-shaped opening 421 before being irradiated on a target object placed on a stage. The stage continuously moves in a predetermined direction (for example, the X direction) when writing a pattern. An oblong shape that can pass through both the opening 411 and the variable-shaped opening 421 in this manner is formed in a pattern writing area of a target object 340. A method of forming an optional shape by passing an electron beam through both the opening 411 and the variable-shaped opening 421 is called a variable-shaped method.
In the electron beam pattern writing described above, more precise linewidth uniformity in a target object plane, for example, in a mask plane. Here, if, in the electron beam pattern forming, a circuit pattern is formed by irradiating a mask to which a resist is applied with an electron beam, a phenomenon called a proximity effect caused by back scattering after an electron beam passes through a resist layer to reach a layer thereunder and then reenters the resist layer may occur. Accordingly, dimension variations in which dimensions deviating from desired dimensions are formed when forming a pattern may occur.
To correct the proximity effect, a whole circuit pattern is divided into small blocks of proximity effect measuring 0.5 μm per side to create a map of influenceability. Then, techniques that can suitably form a circuit pattern of determined area density of 50% and calculate a dose for forming a pattern using a dose (fixed value), a proximity effect influenceability α map, and a proximity effect correction coefficient η map are disclosed by documents (See Published Unexamined Japanese Patent Application No. 2005-195787 (JP-A-2005-195787), for example).
In conventional proximity effect correction calculation, a chip area is divided into calculation areas (blocks) of the same size to perform a correction calculation for each block. For the calculation for each block, the block is further divided into small mesh areas. Also, a pattern area density map that defines a pattern area density obtained by cumulatively adding areas of internal figures cut out by small areas is created for each block. Then, the pattern area density map is used for the proximity effect correction calculation.
Here, the calculation time of pattern area density calculation is proportional to the number of shots. Thus, there is a problem that calculations cannot be performed efficiently due to variations in calculation time for each block because the number of shots varies from block to block of the same size. Therefore, the calculation time for each block can be made substantially equal by changing the size of block so that the number of shots contained in each block becomes substantially equal.
On the other hand, the calculation time of proximity effect correction calculation is proportional to the number of small mesh areas. Thus, the calculation time becomes longer in areas of larger block size and shorter in areas of smaller block size. Therefore, there is a problem that if the block size is made non-uniform for the calculation of pattern area density, the proximity effect correction calculation cannot be performed efficiently due to variations in calculation time for each block. Thus, giving priority to one results in a problem for the other.